This invention relates to bearings. More particularly, this invention is a bearing of the type which has one or more magnetic field detectors for indicating the angular rotation of one member with respect to a second member.
Currently, various detectors such as inductive pick up or variable reluctance detectors are used to detect position, velocity or acceleration signals for rotating elements. These detectors typically measure the change in magnetic field strength as a ferro-magnetic rotor or gear tooth pass the detector. The frequency of the detector signal is used to calculate the rotational speed of the rotating member. These detectors have been added to bearing assemblies in an attempt to save space, increase precision and simplify installation.
In U.S. Pat. No. 3,716,788 to Nishida, a variable reluctance detector is added to a wheel bearing assembly to measure axle speed. A toothed rotor is formed on a revolvable inner bearing ring opposite a toothed stator fixed to the stationary outer bearing ring. The bearing outer ring also supports the magnetic coil pickup which produces a voltage in accordance with the changes in magnetic flux induced by alignment of the rotor and stator teeth during rotation. The frequency of the alternating current produced is in proportion to the rotational speed of the axle. A similar type speed detector is disclosed in U.S. Pat. No. 3,826,933 to Anselmino. The speed detector has a magnetic pickup coil secured to the stationary ring of a bearing while a wheel having ferro-magnetic teeth is secured to the rotatable ring of the roller bearing.
U.S. Pat. No. 4,069,435 to Wannerskog discloses a device for detecting the relative motion in a bearing. The device includes a magnetic pickup coil mounted on the non-rotating outer ring seal of a bearing. A toothed wheel is mounted on the rotating ring of the bearing. As the teeth rotate, the variations in the magnetic field are detected by the magnetic coil pickup. The frequency of the detected variations can be used to calculate velocity and acceleration.
In U.S. Pat. No. 4,688,951 to Guers an electric current is required to create a magnetic field. A complicated electrical system is fixed to one of the two bearing races for creating the magnetic field. The known detector devices described above have many deficiencies. The variance reluctance detectors produce a voltage output signal whose frequency and amplitude are proportional to the speed. At low speeds, the output signal is weak and subject to inaccuracy. Furthermore, when the above detectors are added to bearing assemblies, the assembly size increases due to the additional detector components. The mechanical precision and signal accuracy decreases due to tolerance stack-up, and the overall construction becomes more complex. Also, the assemblies are difficult to install and sometimes require separate mounting steps to install the detector.
New automatic control systems, automotive, for example, require precise rotational speed measurement over complete operating ranges, especially at low speeds or zero speeds. Preferably the speed detectors are also low cost, reliable, compact in construction and easy to install.